In recent years, most of electronic apparatuses such as mobile phones have a camera module mounted thereon, and, among them, many of cameras for front-side photographing have an autofocus function mounted thereon. The autofocus function is a function with which an imaging lens is displaced in accordance with a distance to an object and is focused on the object, and a camera module is provided with a lens driving device in order to realize such an autofocus function.
Examples of the types of lens driving devices include various types such as a type using a stepper motor, a type using a piezoelectric element, and a type using a VCM (Voice Coil Motor), which have already been distributed on the market. Among them, the lens driving devices of the type using a VCM are comparatively inexpensive and highly reliable, and therefore occupy an overwhelming majority in a field of the camera modules having the autofocus function.
Furthermore, a camera module that is provided with an image stabilizer function in addition to the autofocus function has been recognized in the market in recent years. As a device that drives an imaging lens for image stabilization, such a driving device that includes the VCM is also the mainstream, and a lens driving device that drives an imaging lens in three-axis directions for the autofocus function and the image stabilizer function has been proposed.
On the other hand, in a field of camera modules, there is always a demand for increasing the number of pixels in order to obtain an image having higher resolution, and there is a tendency to increase the number of pixels for satisfying such a demand. Accordingly, a diameter of an imaging lens tends to become larger, and the imaging lens tends to be heavier. However, a small size, light weight, low power consumption, and the like are important key words at the same time for a small-sized mobile apparatus such as a mobile phone, and therefore it is difficult to synergistically increase the size of a lens driving device just because the lens driving device drives the large and heavy imaging lens. Furthermore, since priority is put on securing a space in which a display panel such as a liquid crystal display panel, which is larger, and a battery having higher capacity are arranged, there has been an increase in the number of cases where size reduction and thickness reduction of a camera module are desired more than ever.
Each of PTLs 1 and 2 describes a conventional camera module that is provided with a movable portion including an imaging lens which is driven for realizing the autofocus function. PTL 3 describes a conventional camera module that is also provided with the image stabilizer function in addition to the autofocus function.
On the other hand, PTL 4 proposes a conventional camera module that has a configuration in which, in order to reduce weight of a movable portion including imaging lenses which are driven for realizing the autofocus function, the imaging lenses are divided into two groups, and some of the lenses are set to be fixed lenses and only the remaining lens is driven. In the camera module disclosed in PTL 4, a lens that is closest to an image and a lens that is closest to an object are the fixed lenses, and the autofocus function is realized by driving a lens between the fixed lenses. A system in which a lens or a lens group, which is arranged on an inner side, is driven to realize a focusing operation as described above is referred to as an inner focus system. For the camera module disclosed in PTL 4, a case is described where an ultrasonic linear actuator referred to as an SIDM (Smooth Impact Drive Mechanism: registered trademark) is used as a lens driving device for driving such a lens (inner lens) arranged on an inner side. In addition, though it is suggested that a VCM (voice coil motor) is used, a specific configuration thereof is not described.